All textbooks should contain a few deliberately placed errors that students should be capable of detecting. This way if a student is confused he might suspect it is because his textbook is wrong.
Having recently taught a logic course with a recently-revised textbook which has numerous, serious typographical errors I have to say that this strategy runs the serious risk of convincing some students that they are not smart enough to understand the material because they cannot resolve their confusion. This is not a good outcome.
Placing errors late in a sequence of repetitive exercises so that the students have developed some confidence in their ability to apply the material before they hit the error might serve a useful purpose. Errors right at the start of such a sequence can be disastrous, however.
Agreed—a typo in a problem set can turn it from a 15-minute assignment to a 3-hour confusion, and not necessarily to any benefit.